Abaixo está uma instrução que descreve uma tarefa de geração de SQL, combinada com uma entrada que fornece mais contexto sobre os esquemas de tabela disponíveis. Escreva o código SQL que responda adequadamente à solicitação
 ###Instrução: Quantos distritos apresentaram o democrata Nicholas von Stein?
 ###Tabelas: CREATE TABLE pocket_monsters:_diamond__&__pearl_series (pocket_monsters:_diamond__&__pearl_series_id AUTO_INCREMENT PRIMARY KEY, # INT, Japanese title VARCHAR, Rōmaji VARCHAR, Japanese translation VARCHAR, Vocalist VARCHAR, Episodes used VARCHAR) CREATE TABLE owned_and_operated_stations_of_other_networks (owned_and_operated_stations_of_other_networks_id AUTO_INCREMENT PRIMARY KEY, City VARCHAR, State or Territory VARCHAR, Station call sign VARCHAR, Network VARCHAR, Channel number INT, Programs Aired VARCHAR) CREATE TABLE doubles_finals_19_10-9 (doubles_finals_19_10-9_id AUTO_INCREMENT PRIMARY KEY, Outcome VARCHAR, Date INT, Tournament VARCHAR, Surface VARCHAR, Partner VARCHAR, Opponents in the final VARCHAR, Score in the final VARCHAR) CREATE TABLE men_indoor (men_indoor_id AUTO_INCREMENT PRIMARY KEY, Pos. INT, Mark VARCHAR, Athlete VARCHAR, Venue VARCHAR, Date VARCHAR) CREATE TABLE match-up_summary (match-up_summary_id AUTO_INCREMENT PRIMARY KEY, District INT, Incumbent VARCHAR, 2008 Status VARCHAR, Democratic VARCHAR, Republican VARCHAR)  
SELECT COUNT District FROM match-up_summary WHERE Democratic = nicholas von stein